"This just proves their hastiness is fueled by greed not in the best interest for tribes or the Dakotas," Joye Braun, a member of the Cheyenne River Sioux, said in a statement put out by Indigenous Environmental Network, a nonprofit that has opposed Dakota Access.

"Do we have more spills just waiting to happen? This is our home, our land and our water," Braun said.

The Standing Rock Sioux Tribe continues to fight Energy Transfer Partners(ETP) in court in an effort to halt the project's expected opening next month.

"This is what we have said all along: oil pipelines leak and spill," Standing Rock Chairman Dave Archambault II said in a statement about the incident.

Archambault argued that the court must halt the project to protect the tribe as well as the "17 million people whose drinking water is at risk."

Once it's operational, Dakota Access is expected to move nearly half a million barrels of crude oil each day across the Midwest.